custom led vu meter

Discussion in 'The Projects Forum' started by computron, Jun 11, 2012.

  1. computron

    Thread Starter New Member

    Jun 11, 2012
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    I want to build a custom led vu meter. I want it to be very bright. Would the super bright led work that's on ebay? I never built a circuit with chips, resistors and capacitors. I am confident i could do it if i have the parts and a diagram. I bought the lm3915 microchip and holder. Each led will have a 4-6" lead away from the board.
     
  2. Wendy

    Moderator

    Mar 24, 2008
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    Welcome to AAC!

    Modern LEDs are much brighter than they used to be, I would suggest breadboarding it and seeing if it is what you want.
     
  3. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    I have some high efficiency red LEDs that are blinding bright at 10 mA.
     
  4. computron

    Thread Starter New Member

    Jun 11, 2012
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    I am planning on using blue leds for my project. If I cant use super bright then I would use regular leds.
    I was thinking about buying this kit and replacing the red, yellow and green leds with blue. any suggestion?

    http://www.landmelectronics.com/product.cfm/28723/

    velleman k4306
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    "Super bright" LEDs sold on E-bay are probably No-Name-Brand and if there are any brightness spec's they might be exaggerated.
    If the LEDs are very bright then they might be ordinary dim ones in a case that focuses the light into a bright but very narrow beam that can barely be seen if it doesn't shine directly at you.

    The expensive Velleman kit uses a high supply voltage and uses a current of only 5mA in each LED to avoid melting the bar graph IC. 5mA is not bright.
     
  6. computron

    Thread Starter New Member

    Jun 11, 2012
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    Can someone help me understand this schematic. I understand a little but I want to be sure before I start this project. I put letters on points on this image that I need a little bit more understanding.
    I would like to know if these blue leds will work with lm3915.
    http://www.futurlec.com/LED/LED5BULB.shtml


    1) What is the different of A B & C gnds
    2) where do I connect D
    3) I assume E is a variable resistor that will adjust input signal
    4) F or G resistor affect led brightness, I think
     
  7. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    Without some kind of signal processing circuitry to process the audio signal, like an averaging meter or peak detector, it's not really a VU meter it's just an AC voltmeter that isn't really very useful for indicating perceived audio level.... which is what a VU meter is supposed to do.

    http://en.wikipedia.org/wiki/VU_meter

     
  8. Audioguru

    New Member

    Dec 20, 2007
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    Of course. A blue LED has a forward voltage drop of about 3.5V so the minimum supply to the LM3915 must be 1.5V higher at least 5V.

    In my LM3915 VU meter they are connected together and R2 is not used.

    It is the positive power supply for the LEDs. Usually it is the same as DC+. +20V is too high.

    Yes.

    You should read the datasheet for the LM3915. It shows that R3 and R4 form a voltage reference at pin 7 and their current sets the current in the LEDs with a certain formula.
    The datasheet shows 3 simple peak detector circuits.

    EDIT:
    The old blue LEDs you selected are bright because their case focusses the light into a narrow beam that might not be seen if the LEDs are not pointing directly at you. Select modern bright wide angle LEDs instead.
     
  9. GRNDPNDR

    Member

    Mar 1, 2012
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    I use 13,000mcd LEDs from a chineese seller on ebay. They are great LEDs, dirt cheap and bright as hell. they are like $10 for 50 from a place called Light Of Victory LED store (But i think they changed their name to hitechworld or something)
     
  10. Audioguru

    New Member

    Dec 20, 2007
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    I betcha they have a very narrow viewing angle and do not have a detailed datasheet in English.
    They change their name to reduce the number of law suits.
     
  11. GRNDPNDR

    Member

    Mar 1, 2012
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    I'm not entirely sure where you're going with that, but the viewing angle I believe is 15* which is what most LEDs are if I'm not mistaken. I'm also not sure why they would have lawsuits over LEDs? I personally have never had any problems with them and I've used hundreds of the LEDs re-working the switches in the 96/97 cougars and thunderbirds.

    I have yet to find any place else that sells LEDs as bright as 13,000mcd and if they do, they are deadly expensive.
     
  12. Audioguru

    New Member

    Dec 20, 2007
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    Many LEDs have a 40 degrees light beam and therefore are not as bright as a tightly focussed 15 degrees one.
    LEDs in my cheap solar garden lights have a light beam that is 120 degrees and they are very bright.
     
  13. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,026
    I found some cheap Hong Kong LEDs on E-bay that claimed >20,000. They're very bright but as AG points out, very narrowly focused. Very similar to a good flashlight beam, maybe not quite that tight. Anyway, they're blinding at even 5mA if they're on-axis. They're not bad as an indicator off-axis, but a diffuser would help if you want more brightness off-axis. Or just buy a different, wide angle LED.

    Oh, I should add that I had a radio Shack Blue LED to compare to, and the LEDs from Hong Kong probably make 5X more light at a given current, regardless of focusing.
     
  14. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
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    The 3W Luxeon LEDs I use for the tail lights on my bike have a 120 degree viewing angle and are actually blinding bright (don't look at them without the lense in place).
     
  15. computron

    Thread Starter New Member

    Jun 11, 2012
    4
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    My intention is to build a circuit that will make a string of 10+ leds dance with the music. The lm3915 looks like the simplest way of doing this.
     
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